Primary batteries are widely used for many applications. There is a need for high capacity batteries for certain applications such as remote communications, ocean navigation units (long term, low rate discharge) or recharging of secondary batteries. High gravimetric and volumetric capacities are essential for such applications.
Primary batteries with metal anodes (lithium, magnesium, aluminum, etc.) and various cathodes have high capacity. Metal-air batteries, where air oxygen serves as an oxidant in an air diffusion cathode, are known, and they are characterized by a high energy density, a flat discharge voltage, and long shelf storage, when stored dry. They are environmentally safe when properly disposed of, and available at a relatively low cost. The best known of the metal-air batteries are the zinc-air battery and the aluminum-air battery, where zinc or aluminum is oxidized by atmospheric oxygen. The zinc-air battery has a higher volumetric and gravimetric capacity than other widely used batteries, including lithium ion batteries. Aluminum anodes have the closest volumetric and gravimetric capacity to lithium metal (2.98 Ah/g vs. 3.86 Ah/g). However such capacity is still insufficient for some applications.
Lithium has a very high gravimetric capacity but low volumetric capacity (1.98 Ah/cm3), and is very reactive, which makes handling difficult and hazardous, and which, makes lithium-air cell design more complicated.